1. Field of the Invention
The present invention relates generally to water heaters. In particular, the present invention relates to the control of water heaters for proper operation and safety.
2. Discussion of Background
Much of the world has come to depend on having hot water on demand for bathing, laundering, and cooking. Usually this demand is met by water heaters. Water heaters come in two basic types: storage water heaters, which heat water in a tank for use when there is a demand, and instantaneous water heaters, which heat water as it is being drawn through the heater.
Controlling the water heater begins with the temperature of the water it supplies. More specifically, being able to heat the source water to a desired temperature means being able to select that temperature from a range of temperatures and then controlling the water heater so that it does, in fact, heat the water to that temperature, regardless of changes in the many parameters that will affect its operation. Although the temperature of the water leaving the heater is simply a function of the temperature of the water entering the heater and how much net heat is added to it, both the inlet temperature and the amount of heat that is needed will vary. For example, the amount of heat that must be added depends on how well insulated the particular water heater is and how efficiently it transfers heat to the water. Efficiency changes with time as scale builds up on the heat transferring components. Furthermore, the temperature at the outlet may need to be varied depending on how far away from the heater the tap is located. In turn, the amount of heat added is a function of the instantaneous heat addition rate and the duration of heating. Many other factors complicate the control of water temperature, including heat losses, water mixing, overshooting of the setpoint temperature, and so on.
Control is not limited to temperature and the way heat is added. If the water heater uses natural gas as a fuel for combustion to produce heat, control of the flow of gas, ignition of the gas, completeness of combustion, and sensing of gas leaks are also important. There are other factors besides fuel use and delivery that may affect the safe use of the water heater. Furthermore, the response of the control system to a condition that is potentially harmful may vary, depending on the sophistication of the control system. Consequently, there has been considerable development in the control mechanisms of water heaters.
For example, in the area of sensing the presence of harmful gases, including both combustible gases and carbon monoxide, see Teeters"" (U.S. Pat. No. 3,909,816) flame color and carbon monoxide sensor and alarm circuit for use with a water heater, and Comuzie, Jr.""s (U.S. Pat. No. 5,280,802) apparatus for detecting xe2x80x9cspillagexe2x80x9d and xe2x80x9croll-outxe2x80x9d gas fumes of a water heater. Spillage gases are those that result from a blocked flue; roll-out gases are those that occur when there is a backup at the flame of the heater. Park, et al., in U.S. Pat. No. 4,893,113, teach the sensing of carbon monoxide and the detoxifying of the sensed carbon monoxide in a water heater. When combustion gases are detected, it is known to cut off the fuel to the water heater or shut off power, as taught, for example, by Kass, et al. in U.S. Pat. No. 5,189,392. A modicum of control of the flue draft for water heaters is taught by Habegger in U.S. Pat. No. 5,039,006. If his controller is unable to obtain adequate flue draft, its spillage sensors shut down the unit.
Devices for detecting flammable gases in general are known. For example, see Sun""s (U.S. Pat. No. 5,419,358) flammable gas monitoring system for a boiler, Gazzaz""s (U.S. Pat. No. 4,916,437) gas monitoring system for use in a kitchen supplied with gas for cooking, and Risgin, deceased et al.""s (U.S. Pat. No. 4,443,791) multiple gas detection system for industrial environments. The Gazzaz (""437) device will shut off the flow of gas and issue an alarm if a leak is detected. Also, devices for detecting carbon monoxide in apparatus other than water heaters are known, such as Hilt""s (U.S. Pat. No. 5,239,980) forced air furnace control system. Devices for detecting multiple gases, including fuel gases and those resulting from combustion of gases, are also known in arts other than water heater design. For example, see Whittle""s (U.S. Pat. No. 5,379,026) fuel and combustion gas alarm for building occupants, and Polk, et al.""s (U.S. Pat. No. 5,477,913) control system for gas detection used with a heating and air conditioning unit. A shortage of oxygen at a burner can result in inefficient combustion and an excess of harmful byproducts. An oxygen sensor for burners is taught by Wada, et al. in U.S. Pat. No. 4,482,311. Correspondingly, a surplus of oxygen at the flue can indicate incomplete or inefficient combustion. A device that controls combustion, in part from feedback from oxygen levels sensed in a refinery furnace flue and in part by damper control, is taught by Sun in U.S. Pat. No. 4,330,261. Regulation of damper and fuel line to achieve efficient combustion is taught by Williams in U.S. Pat. No. 4,299,554 in a fluid fuel-fired furnace.
Although various problems of controlling a water heater are addressed by others, including those noted above, the focus is the detection of spillage and roll-out gases and not harmful gases generally, including leaking natural gas and propane. Furthermore, attacking the problem of water heater controlxe2x80x94gases, temperature, operationxe2x80x94in piecemeal fashion results in complexity in the overall control system and unnecessary cost and inefficiency.
Therefore, there remains a need for improvements in the approach to control of the various operational systems and safety features of a water heater.
According to its main features and briefly stated, the present invention is a multiple function, solid state control system for a water heater. The control system comprises a control panel having a microprocessor, mounted to the exterior of the water heater, in electrical connection with a flammable gas sensor, positioned proximate to the air intake. Upon detecting a preselected concentration of a flammable gas, the sensor will issue a signal to the control panel which will prevent ignition of the burners, or shut them off if already in operation. A carbon monoxide sensor, positioned proximate to the draft hood, detects the presence of an unacceptable level of carbon monoxide, indicative of a blocked vent pipe, and also sends a signal to the microprocessor which will prevent, or discontinue, the operation of the burners. Both the flammable gas and carbon monoxide detector contain self-diagnostic circuitry which assures proper sensor operation. In addition, circuitry within the microprocessor monitors the service life of the sensors and will cause an alarm to be initiated when the sensors require replacement.
The control system also monitors a variety of different functions necessary for the proper operation of a water heater. Water temperature is monitored and prevented from rising above a preselected temperature. The burner is monitored to assure the existence of a flame during operation. The current being drawn by both the pilot solenoid valve and the main solenoid valve is monitored for proper valve operation.
Ignition control is achieved by monitoring the number of attempts to ignite the pilot light. If ignition is not accomplished in a preselected number of trials, the controller will subsequently block any attempt at ignition until a reset order has been issued. The controller also monitors the current generated from the motor operating the draft hood, assuring that the hood opens, closes, and maintains its proper orientation during the operation of the water heater.
Upon receipt of a signal from any of the above described sensors, the controller will terminate the operation of the burners and issue a visual and/or auditory alarm.
The controller is also programmed to monitor the use of the water heater and establish a pattern of operation. The controller will monitor the operation of the heater for a period of time, preferably seven days, to determine periods of high usage and periods of low usage. After the initial monitoring period, the controller activates the burners to heat the water to the setpoint temperature a predetermined time period prior to the anticipated high-usage period. During periods of low usage, the controller will set back the temperature approximately 15xc2x0 F. to conserve energy. If the pattern of use changes subsequent to the seven day monitoring period, the controller will record the changes and modify the schedule according to the new pattern.
In the event of a malfunction, power outage, or other discontinuity in operation, the controller routes to non-volatile memory all salient information such as water temperature, operational status of the sensors, and the age of the carbon monoxide and flammable gas sensors. Consequently, for routine maintenance or repair, the condition of the water heater and the reason for its malfunction can be readily ascertained.
A major feature of the present invention is the placement of the flammable gas sensor, proximate to the air intake channel. Placement of the sensor in this region enables the sensor to sense the presence of a dangerous concentration of flammable gas and issue a signal to the controller prior to the gas reaching the flame. Consequently, the controller is capable of deactivating or preventing the operation of the burners prior to an explosion.
Another major feature of the present invention is the use of a carbon monoxide detector to determine the blockage of the vent pipe. A vent pipe can become blocked by birds, improper roof installation, rusted pipes, or the like. When this occurs, combustion gases back up below the exit to the flue and are referred to as xe2x80x9cspillagexe2x80x9d gases. These spillage gases contain an unsafe concentration of carbon monoxide. The gases will escape from both the ductwork and burner area of the water heater and enter the surrounding area, causing the danger of injuries and possibly death to individuals in the vicinity. By providing a carbon monoxide sensor, it is possible to detect the presence of an excessive concentration of carbon monoxide and deactivate the burners before the carbon monoxide concentration reaches a hazardous level.
Still another feature of the present invention is safety. The present invention centrally monitors a number of operational conditions that impact safety. Upon issuance of a signal that any of these conditions are outside operating parameters or are failing to function, the controller will halt the operation of the burners and emit an audio and/or visual alarm which details the type of malfunction that has occurred. Consequently, the danger of an explosion, escape of harmful gases, and other hazards associated with the operation of a water heater are minimized. Moreover, by indicating the type of malfunction that has occurred, diagnosis and repair is simplified.
Other features and their advantages will become apparent to those skilled in the design of water heaters from a careful reading of the Detailed Description of Preferred Embodiments accompanied by the drawings.